[PATCH 4/5] freezer cgroup: Fix an RCU warning in cgroup_freezing_or_frozen()

[Li Zefan]

with CONFIG_PROVE_RCU, a warning can be triggered when we
resume from suspend:

...
include/linux/cgroup.h:533 invoked rcu_dereference_check() without protection!
...

task_freezer() calls task_subsys_state(), which needs to be
protected by rcu_read_lock or cgroup_mutex.

Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
 kernel/cgroup_freezer.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 5038f4c..ac76983 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -53,6 +53,7 @@ int cgroup_freezing_or_frozen(struct task_struct *task)
 	struct freezer *freezer;
 	enum freezer_state state;
 
+	rcu_read_lock();
 	task_lock(task);
 	freezer = task_freezer(task);
 	if (!freezer->css.cgroup->parent)
@@ -60,6 +61,7 @@ int cgroup_freezing_or_frozen(struct task_struct *task)
 	else
 		state = freezer->state;
 	task_unlock(task);
+	rcu_read_unlock();
 
 	return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN);
 }
-- 
1.6.3

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